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Abstract:
The thermal dissociation pathways of AsH3 on Ga-rich (4 × 6) and As-rich c(2 × 8) GaAs(100) surfaces have been studied with high-resolution electron energy loss (HREELS), X-ray photoelectron (XPS) and thermal desorption spectroscopy (TDS). Arsine adsorbs molecularly at 115 K and, based on XPS data, the saturation coverage is 0.16 ± 0.04 ML. In TDS, desorption of the parent molecule is accompanied by As-H bond dissociation starting at temperatures as low as 140 K. Of the resulting AsHx (x = 1, 2) and H, part recombines to liberate arsine but approximately 15% of the initial AsH3 coverage dissociates irreversibly resulting in As deposition on the GaAs surface. While on the As-rich surface there is no evidence for Ga-H formation, we do observe transfer of hydrogen from As to Ga sites on the Ga-rich surface. Recombinative hydrogen desorption from Ga-H occurs around 500 K on Ga-rich surfaces, whereas H2 desorbs at higher temperatures (~ 550 K) from As-H on As-rich surfaces. With regard to atomic layer epitaxy (ALE) of GaAs, these results imply that, in the final stages of an As cycle, removal of hydrogen from As sites limits the rate whereas in the initial stages, Ga-H is the reaction intermediate.
